The present invention relates to a method for manufacturing chitosan fiber by means of wet spinning using an aqueous solution of sodium thiocyanate as a solvent.
Because of the necessity of providing a healthy and hygienic environment, many fiber products processed with an antibacterial treatment have been produced. The art of providing antibacterial properties using antibacterial metal carried on zeolite is disclosed in Japanese patent publication Sho-63/054,013 and in Japanese laid-open patent publications Sho-63/175,117 and Hei-01/250,413. Also, a method of applying antibacterial agents of an antibacterial quaternary ammonium salt type to fiber or to cloth has been known in the art.
However, fiber and cloth prepared by such methods often cause inflammation, etc., to human skin depending upon the use, resulting in discomfort and problems in terms of safety and hygiene.
In view of the above, attempts have been made to utilize chitin or chitin derivatives having relatively low toxicity and high safety to human body.
Chitosan, which is one of the derivatives of chitin, is prepared by heating chitin in the presence of an alkali followed by hydrolyzing for deacetylation. Said chitin, which is a polysaccharide having an N-acetyl-D-glucosamine-beta-1-,4-glucoside bond, is contained in crustaceans, such as shrimp and crabs, and insects, such as beetles and grasshoppers, and is available in large quantities in nature. Chitosan has the properties of allowing permeation of water and low-molecular compounds therethrough, exhibiting a good anticoagulant action, and shows a good affinity with tissues of living organisms, rarely causing an undesirable tissue reaction. In view of such characteristics, application of chizosan as a biomaterial has been conducted and its utilization in microcapsule materials, dialysis membrane, artificial organs, surgical materials, etc. has been attempted.
At present, in order to subject chitosan to wet spinning, there is a disclosure in Japanese laid-open publication Sho-56/026,049 of a method in which chitosan is dissolved in an aqueous solution of acetic acid and the resulting solution (a spinning solution) is spun into a mixed solvent of alcohol and water to make into fiber. However, this method has a disadvantage that, when chitosan is dissolved in an aqueous solution of acetic acid, the viscosity of the resulting spinning solution is extremely high, since the intermolecular hydrogen bond of chitosan is strong, whereby the ability of the solution to be spun decreases. In order to improve this disadvantage, there is a proposal in Japanese laid-open patent publication Sho-59/116,418 where a spinning solution is prepared by dissolving chitosan in a mixed solvent of water and dichloroacetic acid or by dissolving acid addition salt of chitosan in water or in a mixed solvent of water and dichloroacetic acid, and the resulting spinning solution is molded/coagulated in an aqueous solution of metal salt followed by treating with a chelate reagent, whereby improvement in the ability of the solution to be spun and acceleration of coagulation of the spinning solution are attempted.
However, some of the chemicals used in the above processes are strongly irritative and cause a danger upon actual use and, therefore, in Japanese laid-open patent publication Sho-60/059,123, chitosan or an acid addition salt thereof is dissolved in a mixture of an aqueous solution of acetic acid and urea whereupon the problem of use of irritative, dangerous chemicals is solved.
Another study in which a specialized solvent such as hexafluoroisopropyl alcohol or hexafluoroacetone is used has also been reported.
In the above-mentioned methods for manufacturing chitosan fiber which have been proposed up to now, chemicals which are toxic to human body, such as being strongly irritative to skin, have been used. Even in the invention of the Japanese laid-open patent publication Sho-60/059,123 wherein such a problem is improved, the strong odor associated with the chemicals in that process is a disadvantage, and upon production on an industrial scale, the method is not practical because of this strong, offensive odor. In addition, the organic acids used are highly corrosive to metal and, therefore, in a process for manufacturing chitosan fiber using acetic acid and dichloroacetic acid as solvents, measures against corrosion are to be taken into consideration. In the case of use of specialized solvents, such solvents are very expensive and, therefore, use of such solvents is also not practical.